A variety of neurological and neuropsychiatric disorders appear to be due to disturbance of the dopaminergic system. Since recent studies indicate that Di-like and D4 dopamine receptor selective antagonists are not effective antipsychotics, there is a renewed focus on D3 dopamine receptors as a target for antipsychotic drugs used in the treatment of schizophrenia. In addition, recent studies suggest that the D3 dopamine receptor subtype might be an important target for the development of agents for pharmacotherapeutics that could be used in the rehabilitation of individuals who abuse cocaine. However, it has been difficult to develop selective D3 receptor compounds that can be used for experimental or clinical studies on the role of the D3 dopamine receptor subtype in neuropsychiatric disorders or drug abuse because the D2 and D3 dopamine receptors have a high degree of amino acid sequence homology within the transmembrane spanning regions, which construct the neutotransmitter binding site. In collaborative studies, our laboratory has identified a series of structurally related compounds that range from 5- to 50-fold selective for the LB compared to the D2 dopamine receptor subtype. The experiments described in this proposal are designed to identify the amino acid residues within the D2 and LB dopamine receptor binding sites that directly interact with the currently available LB selective compounds. This will be accomplished by preparing mutant receptors structurally related to the D2 and LB dopamine receptor subtypes to precisely define the position of the pharmacophore within the neurotranamitter binding site. The results of these studies will 1) provide information on how our current LB dopamine receptor selective compounds bind to the neumtransmitter binding sate and 2) provide additional structural information that will assist us in the design of novel compounds with increased selectivity for LB dopamine receptors